Heat shrinkable plastic products are widely used in the field of film such as a shrinkable packaging, a shrinkable label, and so on due to their shrinking property when heated. Specifically, polyvinylchloride (PVC), polystyrene or polyester based plastic film has been used as a label, a cap seal or a direct packaging for various containers.
However, in case of the polyvinylchloride (PVC) film, hydrogen chloride gas, dioxin precursors and so on are produced when incinerated. Thus, the use of the material is not environmentally desirable. In addition, when the PVC film is used as a shrinkable label for a polyethylene terephthalate (PET) container, the label and the container should be separated for recycling the container.
The polystyrene film has a good stability during a shrinking process and has a good appearance. On the other hand, the polystyrene film is not good in a chemical resistance, and thus special ink compositions should be used to print on the film. In addition, the polystyrene film has a poor storage stability at room temperature, and therefore the dimensions of the film are liable to change due to its natural shrinkage.
The polyester film does not have the drawbacks in an environmental aspect and in the chemical resistance, and is considered as a substitute heat shrinkable film replacing the two above-mentioned materials. As the use of a PET container increases, the use of a shrinkable label made of the polyester film also increases because an additional label separating process is not necessary for recycling the PET container.
However, the conventional heat shrinkable polyester film has a low heat resistance, which requires a new improvement. Specifically, when a shrinkable label made of the heat shrinkable polyester film is affixed on a container, and the container is exposed to heat (for example, when hot drink (60 to 70° C.) is contained in the container), the shrinkable label may be further shrunk and deformed. Therefore, the label can be deformed from its original desired shape.